Treatment of methylene blue by mesoporous Fe/SiO2 prepared from rice husk pyrolytic residues

Silica (SiO2) and iron-incorporated silica (Fe/SiO2) materials are prepared from rice husk pyrolytic residues through alkali treatment, co-precipitation and calcination. The prepared material is characterized by ICP-AES, XRD, FT-IR, UV–vis DRS, XPS, SEM-EDS and TEM, and the results indicate that the prepared materials are mesoporous, where framework and extra-framework iron species concurrently exist in the Fe/SiO2. The prepared materials are applied to treat methylene blue (MB) solution, where influencing factors such as temperature, pH, the dosage of H2O2 and Fe/SiO2 are studied. Under the optimal conditions, Fe/SiO2 shows a much better adsorption effect than SiO2, where Fe/SiO2 can adsorb 85% of MB within only 2 min, and almost 98.8% color is removed within 90 min in the presence of both Fe/SiO2 and H2O2. Only 0.46% iron leaches from Fe/SiO2, and it performs relatively good results in the recycle utilization where almost 90% of chroma is removed within 10 min or 20 min. Hydroxyl radicals are successfully captured by electron paramagnetic resonance (EPR) experiment and it proves that a heterogeneous Fenton-like system form in the presence of both Fe/SiO2 and H2O2, i.e., Fe/SiO2 acts as both adsorbent and catalyst in the treatment process of MB.